Metal-polymer bearings have previously been used in many applications, with grease sometimes added to provide or improve lubrication. These metal-polymer bearings have traditionally shown better wear resistance as compared to metallic bearings when grease is used for lubrication. FIG. 1 shows the improved wear resistance of a metal-polymer bearing (DX=Acetal-lined) as compared to a bronze bearing (660 grade) in a greased application (with repeated grease re-application). As shown in FIGS. 2 and 3, the use of higher performance polymers in metal-polymer bearings (DX10=PA4.6-lined) provide even better wear resistance in both clean grease and abrasive debris-containing grease.
However, a key disadvantage associated with the use of grease in bearing applications is the requirement to re-lubricate. Grease will generally migrate from the load zone, requiring constant maintenance and re-application. Grease also attracts and retains debris, creating the requirement for frequent re-greasing to purge abrasive particles that can harm a bearing, and especially polymer-lined bearings. Insufficient maintenance of a greased bearing can lead to early failure either from lack of lubricant or presence of abrasive debris.
Additionally, grease may migrate from the loaded area of the bearing as a result of load and relative motion. Environmental issues with grease also work against its continued broad-based usage.
The combination of paraffin wax with solid lubricants such as PTFE or other fluoropolymers has previously been identified as having useful lubricating characteristics. However, such combinations have generally been targeted at low temperature applications such as snow skis or other snow-sliding elements. Additionally, the use of such previously known grease-free lubrication methods have not been useful for grease-replacement in the industrial bearing space because of the temperature limitations of the lubricant and the requirement for higher-temperature operation typical in normal industrial bearing lubrication.
Accordingly, a need exists for a grease-free bearing showing wear resistance comparable to, or better than, that exhibited when grease is used as a lubricant, and which is effective at high operating temperatures.